Pulling values from a Java Properties file in order?

Question

I have a properties file where the order of the values is important. I want to be able to iterate through the properties file and output the values based on the order of the

Answer 1

Nope - maps are inherently "unordered".

You could possibly create your own subclass of Properties which overrode setProperty and possibly put, but it would probably get very implementation-specific... Properties is a prime example of bad encapsulation. When I last wrote an extended version (about 10 years ago!) it ended up being hideous and definitely sensitive to the implementation details of Properties.

Answer 2

For those who read this topic recently: just use class PropertiesConfiguration from org.apache.commons:commons-configuration2. I've tested that it keeps properties ordering (because it uses LinkedHashMap internally). Doing:

`
    PropertiesConfiguration properties = new PropertiesConfiguration();
    properties.read(new FileReader("/some/path));
    properties.write(new FileWriter("/some/other/path"));
`

only removes trailing whitespace and unnecessary escapes.

Answer 3

An alternative is just to write your own properties file using LinkedHashMap, here is what I use :

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.LineIterator;

public class OrderedProperties {

    private static Map<String, String> properties = new LinkedHashMap<String, String>();

    private static OrderedProperties instance = null;

    private OrderedProperties() {

    }

    //The propertyFileName is read from the classpath and should be of format : key=value
    public static synchronized OrderedProperties getInstance(String propertyFileName) {
        if (instance == null) {
            instance = new OrderedProperties();
            readPropertiesFile(propertyFileName);
        }
        return instance;
    }

    private static void readPropertiesFile(String propertyFileName){
        LineIterator lineIterator = null;
        try {

            //read file from classpath
            URL url = instance.getClass().getResource(propertyFileName);

            lineIterator = FileUtils.lineIterator(new File(url.getFile()), "UTF-8");
            while (lineIterator.hasNext()) {
                String line = lineIterator.nextLine();

                //Continue to parse if there are blank lines (prevents IndesOutOfBoundsException)
                if (!line.trim().isEmpty()) {
                    List<String> keyValuesPairs = Arrays.asList(line.split("="));
                    properties.put(keyValuesPairs.get(0) , keyValuesPairs.get(1));
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            lineIterator.close();
        }
    }

    public Map<String, String> getProperties() {
        return OrderedProperties.properties;
    }

    public String getProperty(String key) {
        return OrderedProperties.properties.get(key);
    }

}

To use :

    OrderedProperties o = OrderedProperties.getInstance("/project.properties");
    System.out.println(o.getProperty("test"));

Sample properties file (in this case project.properties) :

test=test2

Answer 4

As I see it, Properties is to much bound to Hashtable. I suggest reading it in order to a LinkedHashMap. For that you'll only need to override a single method, Object put(Object key, Object value), disregarding the Properties as a key/value container:

public class InOrderPropertiesLoader<T extends Map<String, String>> {

    private final T map;

    private final Properties properties = new Properties() {
        public Object put(Object key, Object value) {
            map.put((String) key, (String) value);
            return null;
        }

    };

    public InOrderPropertiesLoader(T map) {
        this.map = map;
    }

    public synchronized T load(InputStream inStream) throws IOException {
        properties.load(inStream);

        return map;
    }
}

Usage:

LinkedHashMap<String, String> props = new LinkedHashMap<>();
try (InputStream inputStream = new FileInputStream(file)) {
    new InOrderPropertiesLoader<>(props).load(inputStream);
}

Answer 5

If you can alter the property names your could prefix them with a numeral or other sortable prefix and then sort the Properties KeySet.

Answer 6

Map<String, String> mapFile = new LinkedHashMap<String, String>();
ResourceBundle bundle = ResourceBundle.getBundle(fileName);
TreeSet<String> keySet = new TreeSet<String>(bundle.keySet());
for(String key : keySet){
    System.out.println(key+" "+bundle.getString(key));
    mapFile.put(key, bundle.getString(key));
}

This persist the order of property file